Irradiation continuous-wave laser

By employing a laser for the photoionization (not to be confused with laser desorption/ ionization, where a laser is irradiating a surface, see Section 2.1.21) both sensitivity and selectivity are considerably enhanced. In 1970 the first mass spectrometric analysis of laser photoionized molecular species, namely H2, was performed [54]. Two years later selective two-step photoionization was used to ionize mbidium [55]. Multiphoton ionization mass spectrometry (MPI-MS) was demonstrated in the late 1970s [56—58]. The combination of tunable lasers and MS into a multidimensional analysis tool proved to be a very useful way to investigate excitation and dissociation processes, as well as to obtain mass spectrometric data [59-62]. Because of the pulsed nature of most MPI sources TOF analyzers are preferred, but in combination with continuous wave lasers quadrupole analyzers have been utilized [63]. MPI is performed on species already in the gas phase. The analyte delivery system depends on the application and can be, for example, a GC interface, thermal evaporation from a surface, secondary neutrals from a particle impact event (see Section 2.1.18), or molecular beams that are introduced through a spray interface. There is a multitude of different source geometries. 

Output from both gated continuous wave and pulsed carbon dioxide lasers has been used to desorb ions from surfaces and then to photodissociate them in a Fourier transform ion cyclotron resonance mass spectrometer. Pulsed C02 laser irradiation was most successful in laser desorption experiments, while a gated continuous wave laser was used for a majority of the successful infrared multiphoton dissociation studies. Fragmentation of ions with m/z values in the range of 400-1500 daltons was induced by infrared multiphoton dissociation. Such photodissociation was successfully coupled with laser desorption for several different classes of compounds. Either two sequential pulses from a pulsed carbon dioxide laser (one for desorption and one for dissociation), or one desorption pulse followed by gated continuous wave irradiation to bring about dissociation was used. 

A theoretical study of the photolytic reaction of Ni(CO)4 using LCCTO-Xg has appeared, and the observed luminescence is assigned to emission from the charge-transfer excited fragment Ni(CO)3. Multiple luminescence has been observed from continuous wave laser irradiation of gas-phase Ni(CO)4 at room temperature. Two of the emissions are coupled in an... 

Partial decomposition of explosives [4], upon laser irradiation of the surface, yields a considerable amount of NO2 which can be detected in near real time by the chemiluminescence sensor. It has been found that this process can be done by either using a continuous wave laser (Figure 8) or a pulsed laser (Figure 9). In the last case, more NO2 is evolved upon interrogation of the surface. 

The laser irradiation should then last long enough, hence cw (continuous-wave) lasers might be more appropriate than pulsed lasers, provided that the radiant densities are sufficiently high. 

Figure 8.15 Hematoxylin and eosin staining of muscle tissues, (a) After injection with PEC-modified gold nanorods (b) After injection with PEC-modified gold nanorods followed by continuous-wave laser irradiation (NdiYAC 1064nm,...

Figure 8.16 Tumor growth after photothermal treatment. BALB/c mice with a subcutaneous homograft of B16 melanoma cells were injected with PEG-modified gold nanorods and continuous-wave laser irradiation...

Figure 8.21 Size change of NIPAM-modified gold nanorods. The modified gold nanorods were irradiated with continuous-wave laser light (diode laser, 807 nm, 1 W), after which the sizes were monitored. The size change was seen to be reversible.

Two methods were developed to possibly scale up SWNT production using laser ablation. In 2002, Bolshakov and co-workers reported that SWNTs were synthesized by the continuous-wave laser powder method, which is based on the introduction of mixed graphite and Ni/Co powders into 1100 °C hot argon gas stream irradiated coaxially by a 2kW continuous-wave CO2 laser. Because the particles were of micrometer size, the thermal conductivity losses were significantly decreased and more energy by effective ablation was achieved. The generation rate of the soot product was 5 gh and the SWNT abimdance in the soot was 20-40% besides, the diameter of the as-prepared CNTs was 1.2-1.3 nm (Figure 12). 

New impetus was given to photomedicine by development of lasers that are compatible with the clinical environment. These include HeNe, Ar ion, mby, and tunable dye lasers operating in the continuous wave (cw) mode. Prior to the advent of lasers in medicine, only the treatment of newborn jaundice, and the appHcation of long wavelength uv irradiation in conjunction with adininistration (or topical appHcation) of psoralen class sensitizers to treatment of skin diseases (86), principally psoriasis, were clinically important phototherapies. 

UFPs of the Fe-N system can be synthesized from iron pentacarbonyl Fe(CO)s] and NH3 as reactants by a IOOO-W continuous wave C02 laser irradiation. The NH, gas is the absorbent of the laser beam in this case. At the lower synthesis temperature, below 650°C, UFPs of y -Fe4N with particle size of 10-25 nm grew dominantly. Above 1150°C, however, the growth of y-Fe UFPs with larger particle size of 30-100 nm was predominant (73). Iron carbonitride (lCN) UFPs were also synthesized from the ternary reactants of Fe(CO)s, NH3, and C2H i. The structure oflCN UFPs was hexagonal with e-Fe3(N,C) phase. A large saturation magnetization up to 142 emu/g was obtained and was ascribed to the carbon layer on 1CN UFPs (74). 

Under UV-laser irradiation, photosensitive multifunctional acrylate resins become rapidly cross-linked and completely insoluble. The extent of the reaction was followed continuously by both UV and IR spectroscopy in order to evaluate the rate and quantum yield of the laser-induced polymerization of these photoresist systems. Two basic types of lasers emitting in the UV range were employed, either a continuous wave (C.W.) argon-ion laser, or a pulsed nitrogen laser. 

As an example, the MFEs observed for the anaerobic photolysis of AdoCbl in various solvents by Orison s group [10] will be introduced below. For continuous-wave photolysis, they irradiated AdoCbl in 75%(v/v) glycerol in water (tj/T/o = 30), 20%(w/v) Ficoll-400 WVo = 30), and water (77/770 = 1) at 20°C with an Ar" laser (514nm) and measured the quantum yield (d>) of the decomposition of AdoCbl as a function of B by monitoring the absorbance of AdoCbl . Fig. 15-2 shows the observed MFEs on 0. From this figure, they found that the 0 values in glycerol and Ficoll-400 decreased by nearly 2-fold as B was... 

Perhaps the most likely immediate commercial application of carbonyl fluoride, however, arises from its spectroscopic properties. Irradiation of mixtures of COF, and H, (or D,), over a wide pressure range and at ambient temperature, with the multiline output of a continuous wave CO, laser, results in the generation of excited state HF (DF) which lases [1387]. Energy transfer from the R, line (970 cm" ) of CO, (which is close in energy to the c, band of COF,) causes the dissociation of the COF, to CO and two excited state fluorine atoms which subsequentiy react with the dihydrogen (or dideuterium). However, COF, itself has been found to effect rapid vibrational de-excitation of HF [239], an observation that suggests that the COF,/H, route to the HF laser may be of limited practicality. 

The reactant gaseous streams are irradiated by a continuous-wave C02 laser beam. The laser power is usually between 600 and 1500 W, and the laser beam in the left reaction zone is typically 10 to 11 mm in diameter, while the right one is 9 to 10 mm in diameter. The chemical reaction of the HMDS precursor results in a bright yellow flame. The powders are conducted into a filter holder for collection driven by the vacuum pump. 

Fluorescence intensity measurements are performed by irradiating the trapped ions with 532 nm light (frequency doubled) from a continuous wave Nd YAG laser for 100 ms at an intensity of 130 W cm . The fluorescence data exhibit routinely a S/N ratio in the range of 100-400 for ca 200 ions in the laser interaction volume. An example of this sensitivity is indicated in Figure 7.15 for measurements of Rhodamine 640 fluorescence vs the number of interacting ions excited by 532 nm with an intensity of ca 260 W cm. The use of such small numbers of ions minimizes... 

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